Photochemical preparation of benzene hexachloride



Patented June 27, 1958 PHOTOCHEMICAL PREPARATION OF BENZENE HECHLOE MaxGonzo, Forest-Brussels, Belgium, assignor to Solvay & Cie, companyBrussels, Belgium, a

Belgian No Drawing. Application November 6, 1947, Se-

iisal No. 784,503. In Belgium November 20,

4 Claims. (or. 204-163) This invention relates to the preparation of amixture of benzene hexachlorides free from substitution products andpossessing improved insecticidal properties.

According to the known processes of preparing benzene hexachloride bychlorination of benzene in the presence of light, the operation iscarried out in the liquid phase or in the vapor phase at temperaturesabove the crystallization temperature of benzene. Under these conditionsa more or less important portion of the chlorine is consumed bysubstitution and the reaction is accompanied by an evolution of hydrogenchloride.

In addition to the loss in chlorine and benzene, the production ofsubstitution products has serious drawbacks. They have been heldresponsible for the characteristic unpleasant odor of the productobtained by these processes. Furthermore, such substitution reactions inthe continuous production of benzene hexachloride give rise to seriousdimculties owing-to the fact that the circulating benzene must beperiodically freed from the substitution products. In order to avoid theformation of these products, a process of chlorinating benzene withliquid chlorine in the absence of light has been proposed, as describedin United States Patent No. 2,010,841, but an inconvenience of thisprocess is that it requires either the use of pressure, or themaintenance of a temperature lower than 34 0., this being the boilingpoint of chlorine at atmospheric pressure.

The object of the present invention is to obtain benzene hexachloridefree from substitution products and to avoid the above inconveniences.This is attained according to this invention by carrying out thechlorination in the presence of light, in an inert solvent containingthe benzene dissolved therein, and at a temperature between thecrystallizing temperature of benzene (+6 C.) and the crystallizationtemperature of its mixture with said solvent.

As an inert solvent, I preferably use carbon tetrachloride, which formswith benzene an eutectic mixture containing 15% of CcHs and having asolidification point of about 47 C. In practice I may use a mixture, thebenzene concentration of which is lower than or equal to saturation atthe operating temperature.

The invention is not limited to the use, as solvents, of productssaturated with chlorine but it also applies to any solvent for benzenethat is indifi'erent with respect to chlorine under the operatingconditions of the process.

In discontinuous operation, crystals of CC14 may appear when, in theproduction of CsHsCls, the solution becomes exhausted in benzene and su-Dersaturated with CC14. This however will seldom occur as thesolubilities of benzene hexachlorides are such that the crystals ofCeHsCle will appear before the crystals of C014. However in order topreclude this phenomenon and also to maintain constant the concentrationof the dissolved benzene, it is recommended that a mixture be used inwhich this concentration is greater than that corresponding tosaturation at operating temperatur In that case, the crystals of benzenein suspension form a reserve and dissolve in proportion to the formationof benzene hexachloride. If this reserve is judiciously determined,there will remain in suspension at the end of the chlorination onlycrystals of CeHsCle.

Example 1 In a receptacle containing no selective catalyst forsubstitution reactions, 300 gr. of a mixture containing C014 and 30%benzene are introduced. The mixture is cooled to 20 C. and CO2 is blownthereinto. The reactor is lighted by a mercury vapor lamp and in 40minutes 84 gr. of chlorine gas are introduced in the form of a gaseousmixture containing 10% C02.

The coloring due to dissolved chlorine disappears from the verybeginning of the operation. No evolution of HCl is observed and thefinal product of chlorination is neutral. By separation by means ofwater vapor, a mixture of henzene hexachloride isomers is obtained thatis free from odor and possesses remarkable insecticidal properties.

The process can easily be carried out continuously by operating in amanner similar to that described in my co-pending patent applicationSer. No. 692,722 filed August 23, 1946.

Example 2 In a. liquid mixture of benzene and solvent saturated withbenzene hexachloride at -40 C. and lighted by a mercury vapor lamp,there is imjected at 20 C. benzene and chlorine gas in stoichiometricamounts until the solution is sat-- urated at -20 C. The solution thenflows into a decanter-crystallizer cooled at 40 C. where the crystalsformed are separated and the solution is returned integrally to thechlorinating apparatus. The total absence of substitution reactionsmakes it possible to dispense with the purification operations necessaryin previous processes.

When a particularly .well de-odorized product is desired it isrecommended that the benzene be carefully purified before use asspecified in my co-pending patent application Ser. No. 734,239 filedMarch 12, 1947. For the same purpose and for uniform reaction, it isadvisable to operate in the complete absence of oxygen both in the gaschamber and with respect to the materials used for carrying out thereaction.

I claim:

1. In a process of preparing benzene hexachloride by chlorination ofbenzene with chlorine gas, dissolving benzene in an organic solvent ofthe aliphatic series which is liquid at 6 C. and is substantiallyindifierent to chlorine under operating conditions, and carrying out thechlorination under irradiation by light at a temperature between 6 C.and the crystallizating temperature of the solution of benzene in saidsolvent.

2. In a process of preparing benzene hexachloride by chlorination ofbenzene with chlorine gas, dissolving benzene in carbon tetrachloride,and carrying out the chlorination under irradiation by light at atemperature between 6 C. and the crystallizing temperature of thesolution of benzene in said carbon tetrachloride.

3. In a process as defined in claim 1, maintaining benzene crystals insuspension in the solution whereby said benzene crystals will dissolvegrad- -ually in said solution as the dissolved benzene is transformedinto benzene hexachloride, thereby The following references are ofrecord in the file of this patent:

UNITED STATES PA'I'ENTS Number Name Date 2,010,841 Bender Aug. 13, 19352,218,148 Hardie Oct. 15, 1940 2,438,900 Cooke et a1 Apr. 6, 1948FOREIGN PATENTS Number Country Date 504,569 Great Britain Oct. 26, 1938OTHER REFERENCES Slade, Chemistry and Industry, Oct. 13, 1945, DP.314-319.

1. IN A PROCESS OF PREPARING BENZENE HEXACHLORIDE BY CHLORINATION OFBENZENE WITH CHLORINE GAS, DISSOLVING BENZENE IN AN ORGANIC SOLVENT OFTHE ALIPHATIC SERIES WHICH IS LIQUID AT 6*C. AND IS SUBSTANTIALLYINDIFFERENT TO CHLORINE UNDER OPERATING CONDITIONS, AND CARRYING OUT THECHLORINATION UNDER IRRADIATION BY LIGHT AT A TEMPERATURE BETWEEN 6*C.AND THE CRYSTALLIZATING TEMPERATURE OF THE SOLUTION OF BENZENE IN SAIDSOLVENT.